My original wiper motor works just fine. The park position is to turn the knob on the dash fully counterclockwise, and clockwise is on high. In between varies the speed of the wipers. When you turn it all the way counterclockwise the wipers park from wherever they were when you twisted the knob.
You will not hurt the truck or the wiper motor by leaving it on when the wipers are stuck. It does not pull enough vacuum to affect the engine and the wiper motor is a pretty tough little mechanism. They work pretty well when rebuilt.
